Silicon-carbon composite, method of preparation, secondary battery, and electric device

Abstract

The application provides a silicon-carbon composite material, a preparation method, a secondary battery and an electric device. The silicon-carbon composite material comprises an internal region and an external region, the internal region is mainly composed of silicon-containing material particles, and the external region is mainly composed of carbon-based material particles. The silicon-carbon composite material has excellent specific capacity, and can improve the high-temperature storage performance and cycle stability of the battery.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a silicon-carbon composite material, a preparation method, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] With the widespread application of rechargeable batteries, higher requirements are being placed on their energy density. Silicon-carbon composite materials can improve the energy density of batteries, but they often degrade the battery's storage performance and cycle performance. Therefore, existing silicon-carbon composite materials still need improvement. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to provide a silicon-carbon composite material that has excellent specific capacity while improving the high-temperature storage performance and cycle stability of the battery.

[0005] The first aspect of this application provides a silicon-carbon composite material, which includes an inner region and an outer region, wherein the inner region is mainly composed of silicon-containing material particles and the outer region is mainly composed of carbon-based material particles.

[0006] Silicon has a higher specific capacity than carbon-based materials, but its high surface reactivity makes it prone to electrolyte decomposition on the silicon anode surface, leading to a decline in its storage performance. Furthermore, the lithium storage mechanism of silicon anodes dictates significant volume expansion and contraction during lithium insertion / extraction, which not only deteriorates battery cycle performance but also causes continuous cracking and formation of the solid electrolyte interphase (SEI) film, continuously consuming active ions and further worsening battery storage performance. While carbon-based materials have lower surface activity and structural stability compared to silicon, they cannot further improve battery energy density. Therefore, the silicon-carbon composite material provided in this application is a secondary particle structure where the internal region is mainly composed of silicon-containing material particles and the external region is mainly composed of carbon-based material particles. This structure enables the battery to achieve excellent energy density while simultaneously improving battery storage performance by reducing the surface activity of the silicon-carbon composite material and isolating silicon from the electrolyte. Additionally, the high strength of the carbon-based material particles in the external region inhibits the volume expansion of the silicon-containing material particles, enhancing the structural stability of the silicon-carbon composite material and further improving the battery's cycle stability.

[0007] Compared to silicon-carbon composite materials that directly mix silicon-containing material particles with carbon-based material particles or are secondary particles that are uniformly distributed, the silicon-carbon composite material of this application can not only isolate silicon from the electrolyte, but also reserve space for the volume expansion of silicon-containing material particles by leaving gaps, thereby improving the battery's storage performance and cycle stability, while also taking into account excellent energy density.

[0008] In any embodiment, the number of silicon-containing material particles in the internal region is less than or equal to 3, and can be selected as 1-2.

[0009] When the number of silicon-containing material particles in the internal region is within the above range, it is beneficial for the carbon-based material particles to densely encapsulate the silicon-containing material particles, and to control the particle size of the finished silicon-carbon composite material within a suitable range. This reduces the contact between silicon and electrolyte, improves the dynamic performance of the battery, and also meets the processing performance requirements of silicon-carbon composite materials during negative electrode slurry homogenization and negative electrode coating, so that the battery can take into account excellent storage performance, cycle stability and dynamic performance.

[0010] In any embodiment, the mass percentage of silicon in the region r / 2 from the geometric center of the silicon-carbon composite material is greater than or equal to 30%, and can be selected as 35%-45%, where r represents the minor axis of the silicon-carbon composite material.

[0011] When the mass percentage of silicon in the region r / 2 from the geometric center of the silicon-carbon composite material is within the above range, the battery can achieve excellent energy density, storage performance, and cycle stability.

[0012] In any embodiment, the carbon element mass ratio in the region where the outer surface of the silicon-carbon composite material extends inward by a distance of r / 2 is greater than or equal to 80%, and can be selected as 90%-100%, where r represents the minor diameter of the silicon-carbon composite material.

[0013] When the mass percentage of carbon element in the region extending from the outer surface of the silicon-carbon composite material to the inner surface at a distance of r / 2 is within the above range, the silicon-carbon composite material can isolate silicon from the electrolyte, suppress the volume change of silicon during the lithium insertion / extraction process, and improve the storage performance and cycle stability of the battery.

[0014] In any embodiment, the outer region of the silicon-carbon composite material further includes an amorphous carbon coating layer.

[0015] The amorphous carbon coating layer in the outer region can further isolate the silicon from the electrolyte and reduce the specific surface area of ​​the silicon-carbon composite material. This avoids the secondary particles from having an uneven surface, which would lead to an excessively large specific surface area of ​​the silicon-carbon composite material, increase the contact area with the electrolyte, and reduce the amount of active ions consumed in the formation of the SEI film. As a result, the battery's storage performance, cycle stability, and first-time efficiency are comprehensively improved.

[0016] In any embodiment, the Dv50 of the silicon-containing material particles is greater than or equal to the Dv50 of the carbon-based material particles.

[0017] The Dv50 of silicon-containing material particles is greater than or equal to that of carbon-based material particles, which helps to improve the integrity of the silicon-containing material particles coated by carbon-based material particles, thereby improving the storage performance of the battery.

[0018] In any embodiment, the Dv50 of the silicon-containing material particles is less than or equal to 5 μm.

[0019] When the Dv50 of silicon-containing material particles is within the above range, it is beneficial to control the particle size of the finished silicon-carbon composite material within a suitable range, which results in good electrode processing performance and kinetic performance.

[0020] In any embodiment, the Dv50 of the carbon-based material particles is less than or equal to 5 μm.

[0021] When the particle size of carbon-based material particles is within the above range, the integrity of the carbon-based material particles coating the silicon-containing material particles can be improved, and it is also beneficial to control the particle size of the finished silicon-carbon composite material within a suitable range, so as to meet the performance requirements of electrode processing and improve the storage performance and dynamic performance of the battery.

[0022] In any embodiment, the silicon-containing material particles include at least one of elemental silicon, silicon-oxygen materials, silicon-carbon materials, and silicon-metal alloys. Optionally, the silicon-containing material particles include silicon-carbon materials.

[0023] In any embodiment, the carbon-based material particles include at least one of artificial graphite and natural graphite; optionally, the carbon-based material particles include artificial graphite.

[0024] In any embodiment, the silicon-containing material particles include a carbon substrate with a porous structure and a silicon-based material disposed in the porous structure of the carbon substrate.

[0025] The porous structure of the carbon substrate provides attachment sites for silicon-based materials, enabling large-scale silicon storage. Silicon-based materials uniformly dispersed within the porous structure of the carbon substrate are less prone to agglomeration. Furthermore, the carbon substrate mitigates the volume changes of silicon-based materials within the porous structure during lithium insertion / extraction and can withstand the stress caused by these volume changes. This results in silicon-containing material particles exhibiting low expansion rates and high stability, improving their capacity, storage performance, and cycle stability. The internal region of the silicon-carbon composite material contains silicon-containing material particles with the aforementioned structure, which not only increases battery capacity but also prevents cracking during cycling due to excessive internal volume expansion, thereby enhancing the battery's storage performance and cycle stability.

[0026] In any embodiment, the pore structure includes micropores with a pore size of less than 2 nm, mesopores with a pore size of 2 nm to 50 nm, and macropores with a pore size of more than 50 nm.

[0027] The aforementioned porous structure in the carbon substrate facilitates the adhesion of silicon-based materials within the porous structure and effectively limits the volume expansion of the silicon-based materials attached to the porous structure. Moreover, the expanded silicon-based materials do not cause significant damage to the porous structure of the carbon substrate, thereby increasing the particle capacity of silicon-containing materials while ensuring structural stability.

[0028] In any embodiment, the pore volume of the micropore is greater than or equal to 0.5 cm³. 3 / g, can be selected as 0.6cm 3 / g-0.9cm 3 / g.

[0029] By controlling the pore volume of micropores in carbon substrates, it is beneficial for silicon-containing precursors to enter the pore structure of carbon substrates, reducing the risk of silicon deposition on the surface of carbon substrates and improving the specific capacity and storage performance of silicon-containing material particles.

[0030] In any embodiment, the average pore size of the carbon substrate is less than or equal to 5 nm, and can be selected as 1 nm to 3.5 nm.

[0031] When the average pore size of the carbon substrate is within the above range, it helps the silicon-based material to adhere, and the carbon substrate can limit the volume expansion of the silicon-based material in the pores. The expanded silicon-based material will not cause damage to the porous carbon matrix structure, thereby improving the capacity and structural stability of the silicon-containing material particles, and the battery has excellent storage performance and cycle stability.

[0032] In any embodiment, the specific surface area of ​​the carbon substrate is greater than or equal to 1200 m². 2 / g, optional 1500m 2 / g-1800m 2 / g.

[0033] The carbon substrate has a specific surface area within the above range. The carbon substrate has excellent pore volume, providing more deposition sites for silicon-based materials, which is beneficial to improving the specific capacity of silicon-containing material particles.

[0034] In any embodiment, the silicon-based material includes at least one of elemental silicon, silicon-oxygen materials, silicon-carbon materials, and silicon-metal alloys; the carbon substrate includes at least one of graphite, soft carbon, and hard carbon.

[0035] In any embodiment, the silicon-based material particles include silicon grains, optionally with a size of less than or equal to 10 nm, or optionally with a size of less than or equal to 3 nm.

[0036] By keeping the size of silicon grains within the above range, it is possible to avoid excessive local enrichment of silicon elements due to excessively large grain size, which could cause the silicon-containing material particles to expand significantly during lithium intercalation and lead to cracking. This is beneficial for improving the storage performance and cycle stability of the battery.

[0037] In any embodiment, the porosity of the silicon-carbon composite material is 20%-45%, optionally 20%-35%.

[0038] The porosity of the silicon-carbon composite material is within the above range, which leaves room for the volume change that occurs when silicon-based material particles in the internal region are inserted or extracted with lithium. While taking into account the excellent specific capacity, it can also improve the structural stability of the silicon-carbon composite material, thereby improving the energy density, storage performance and cycle stability of the battery.

[0039] In any embodiment, the volume distribution particle size Dv50 of the silicon-carbon composite material is less than or equal to 16 μm, and can be selected as 8 μm-16 μm.

[0040] When the Dv50 of silicon-carbon composite materials is within the above range, the materials have excellent kinetic properties and electrode processing properties, which are beneficial to improving the storage performance and cycle stability of batteries.

[0041] In any embodiment, the particle size distribution (Dv90-Dv10) / Dv50 of the silicon-carbon composite material is 0.5-1.8, and can be optionally 0.8-1.5.

[0042] When the particle size distribution of silicon-carbon composite materials is within the above range, the overall average particle size of the silicon-carbon composite material is relatively moderate and the particle size distribution is relatively uniform, which is beneficial to improving the uniformity of the overall performance of silicon-carbon composite materials.

[0043] In any embodiment, the powder compaction density of the silicon-carbon composite material at 49000 N is 0.7 g / cm³. 3 -1.3g / cm 3 0.95g / cm³ is an optional value. 3 -1.1g / cm 3 .

[0044] When the powder compaction density of silicon-carbon composite materials is within the above-mentioned range, the negative electrode sheet has a higher compaction density, which further improves the energy density of the battery. In addition, the negative electrode film layer has a strong ability to maintain the pore structure during cycling, and the electrolyte wettability of the negative electrode sheet is better, which is beneficial to improving the battery's storage performance and cycle stability.

[0045] In any embodiment, the specific surface area of ​​the silicon-carbon composite material is less than or equal to 6 m². 2 / g, can be less than or equal to 4.5m 2 / g.

[0046] When the specific surface area of ​​the silicon-carbon composite material is within the above range, it helps to further reduce the contact area between the silicon-carbon composite material and the electrolyte, reduce the consumption of active ions by the formation of the SEI film, and improve the battery's initial efficiency, storage performance and cycle stability.

[0047] The second aspect of this application provides a method for preparing a silicon-carbon composite material, comprising the following steps: providing silicon-containing material particles and carbon-based material particles; performing a first spray granulation on the silicon-containing material particles and a binder to obtain a first intermediate product; spraying carbon-based material particles onto the surface of the first intermediate product to perform a second spray granulation to prepare the silicon-carbon composite material; wherein the silicon-carbon composite material includes an internal region and an external region, the internal region being mainly composed of silicon-containing material particles, and the external region being mainly composed of carbon-based material particles.

[0048] The silicon-containing material particles and binder are first spray-granulated to control the particle size of the silicon-containing material particles in the internal region of the silicon-carbon composite material, resulting in a first intermediate product in which the silicon-containing material particles are uniformly coated with the binder. By second spray-granulating carbon-based material particles onto the surface of the first intermediate product, secondary particles are obtained, consisting mainly of silicon-containing material particles internally and carbon-based material particles externally, with the carbon-based material particles tightly coating the silicon-containing material particles. Compared to methods that simultaneously mix and granulate silicon-containing material particles, binder, and carbon-based material particles, this two-step granulation method achieves a state where the silicon-containing material particles are completely coated with carbon-based material particles, isolating silicon from contact with the electrolyte, and allowing for the control of the porosity of the silicon-carbon composite material, thereby improving the battery's storage performance and cycle stability.

[0049] In any embodiment, silicon-containing material particles are prepared by the following steps: providing a gas containing a silicon precursor to a carbon substrate having a porous structure; and generating a silicon-based material attached to the porous structure from the silicon precursor by chemical vapor deposition to obtain silicon-containing material particles.

[0050] In any embodiment, the mass ratio of silicon particles to binder is 1:2 to 2:1.

[0051] When the mass ratio of silicon-containing material particles to binder is within the above range, there is a good bonding effect between the silicon-containing material particles and the carbon-based material particles. When the particle size of the finished silicon-carbon composite material is within a suitable range, the battery has good storage performance and cycle stability while also having excellent energy density.

[0052] In any embodiment, the mass ratio of silicon particles to carbon-based material particles is 1:12 to 1:6.

[0053] When the mass ratio of silicon-containing material particles to carbon-based material particles is within the above range, the carbon-based material particles form a complete coating layer on the surface of the silicon-containing material particles, isolating silicon from contact with the electrolyte. Furthermore, the silicon-carbon composite material will not reduce its specific capacity due to excessive coating caused by an excessive proportion of carbon-based material particles. As a result, the battery has excellent energy density, storage performance, and cycle stability.

[0054] In any embodiment, the temperature difference between the inlet air temperature and the outlet air temperature of the first spray granulation is no greater than 60°C.

[0055] Spray granulation relies on hot air to dry materials, and the drying state of the intermediate product is controlled by adjusting the temperature of the hot air. Because the temperature of hot air drying is greatly affected by the environment, and the chamber only provides insulation without heating, the temperature inside the chamber is not an exact temperature, but rather a temperature range. Setting the difference between the inlet and outlet air temperatures within this range ensures that the chamber temperature remains within a suitable range, preventing the actual temperature inside the chamber from being too low due to an excessively large temperature difference.

[0056] In any embodiment, the inlet air temperature of the first spray granulation is 110°C-150°C.

[0057] The inlet air temperature is the initial heat source in the chamber. Spray granulation relies on the inlet air to dry the material, ensuring that the silicon-containing material particles coated with the binder are in a semi-dry state. This prevents the silicon-containing material particles from sticking together due to excessively low temperature and moisture, which would result in larger silicon-containing material particle sizes in the internal regions of the finished silicon-carbon composite material, leading to an overall larger particle size in the finished product. Alternatively, excessively high temperature and dryness would prevent the next process from proceeding. Within the aforementioned inlet air temperature range, the silicon-carbon composite material exhibits good kinetic properties and electrode processing performance.

[0058] In any embodiment, the outlet air temperature of the first spray granulation is 50°C-90°C.

[0059] The outlet air temperature is the result of comprehensive consideration of heat, and is determined by factors such as the inlet air temperature and the feeding rate. Setting the outlet air temperature of the first spray granulation within this range can avoid the temperature difference between the outlet air temperature and the inlet air temperature being too large, which would cause the temperature inside the chamber to be too low. It can also further ensure that the first intermediate product is in a semi-dry state, which is beneficial for it to proceed to the next process.

[0060] In any embodiment, the feed air pressure of the first spray granulation is 250KPa-350KPa, and can be selected as 280KPa-320KPa.

[0061] The feed air pressure in the first spray granulation is a crucial step in controlling the particle size of the finished silicon-carbon composite material. When the feed air pressure is within the aforementioned range, the number and size of the sprayed silicon-containing material particles can be controlled within a suitable range. This avoids excessively large particle sizes due to low air pressure, which would lead to an overly large finished silicon-carbon composite material particle size, deteriorating the kinetic properties and electrode processing performance of the silicon-carbon composite material. It also avoids situations where excessively high air pressure causes some silicon-containing material particles to become stuck at the spray nozzle and fail to be sprayed. When the feed air pressure in the first spray granulation is within the aforementioned range, the particle size of the sprayed silicon-containing material is kept within a suitable range, ensuring that the number of silicon-containing material particles in the internal region of the silicon-carbon composite material does not exceed three. This is beneficial for improving the storage performance and electrode processing performance of the silicon-carbon composite material.

[0062] In any embodiment, the temperature difference between the inlet and outlet air temperatures of the second spray granulation is 20°C-40°C.

[0063] In any embodiment, the inlet air temperature for the second spray granulation is 170°C-280°C.

[0064] The inlet air temperature in the second spray granulation step is crucial for controlling the strength and structural stability of the silicon-carbon composite material. Because the first intermediate product has a certain viscosity, it needs to be rapidly coated with carbon-based material particles to form secondary particles and then dried. This prevents the first intermediate product and secondary particles from agglomerating or undergoing secondary bonding due to excessively low temperatures; it also prevents the binder from shrinking too quickly or failing due to excessively high temperatures, thus failing to achieve a good bonding effect. When the inlet air temperature of the second spray granulation is within this range, the prepared silicon-carbon composite material exhibits suitable particle size, excellent strength, and structural stability, playing a role in consistently improving storage performance and cycle performance throughout the battery's lifespan.

[0065] In any embodiment, the outlet air temperature of the second spray granulation is 130°C-240°C.

[0066] In any embodiment, the feed air pressure of the second spray granulation is 150KPa-260KPa, and can be selected as 180KPa-210KPa.

[0067] The feed pressure of the second spray granulation is a key step in controlling the integrity and uniformity of the carbon-based material particles coating the silicon-containing material particles. When the feed pressure of the second spray granulation is within the above-mentioned range, it can improve the storage performance and cycle stability of the battery. It can avoid the situation where the feed rate is too fast due to excessive pressure, resulting in too many carbon-based material particles coating the silicon-containing material, and the particle size of the finished silicon-carbon composite material is too large, which would deteriorate the kinetic performance, electrode processing performance and specific capacity of the silicon-carbon composite material. It can also avoid the situation where the feed rate is too slow due to insufficient pressure, resulting in some silicon-containing material particles not being completely coated by the carbon-based material particles, failing to completely isolate the silicon from the electrolyte, and weakening the storage performance of the silicon-carbon composite material.

[0068] In any embodiment, the preparation method of the silicon-carbon composite material further includes: after the second spray granulation, introducing a gaseous carbon source, followed by gas phase coating and carbonization to obtain the silicon-carbon composite material.

[0069] The secondary particles formed by coating silicon-containing materials with carbon-based material particles have more uneven surfaces and a larger specific surface area. After carbon coating, the specific surface area of ​​silicon-carbon composite materials can be controlled within a suitable range, enabling the battery to have excellent storage performance, cycle stability and first-time efficiency. In addition, the carbon coating layer in the outer region can further reduce the possibility of silicon contacting the electrolyte, further improving the battery's storage performance.

[0070] In any embodiment, the gaseous carbon source includes a gaseous hydrocarbon alkane, which may be at least one of methane, ethylene, and acetylene.

[0071] The temperature at which the aforementioned gaseous carbon source decomposes to form the carbon coating layer is within a suitable range, satisfying the temperature requirements of each component of the silicon-carbon composite material.

[0072] In any embodiment, the carbonization temperature is 400°C-800°C.

[0073] When the carbonization temperature is within the above range, the gaseous carbon source can decompose to produce carbides that coat the surface of the secondary particles, forming a carbon coating layer. This reduces the specific surface area of ​​the secondary particles and further isolates the silicon from the electrolyte, improving the battery's storage performance and cycle stability. It also avoids the formation of silicon carbide from silicon-containing material particles due to excessively high temperatures, thus achieving the goal of not losing the specific capacity of the silicon-carbon composite material.

[0074] In any embodiment, the carbonization time is 0.2h-2h.

[0075] When the carbonization time is within the above range, the silicon-carbon composite material has a suitable specific surface area and excellent capacity. This avoids the problem of insufficient amorphous carbon coating due to too short a time, which would prevent the secondary particle surface from being completely covered and thus reduce the specific surface area. It also avoids the risk of silicon forming silicon carbide due to excessively long carbonization time, which would cause a loss of capacity in the silicon-carbon composite material.

[0076] In any embodiment, the protective gas during carbonization is nitrogen or argon. Optionally, the gaseous carbon source to protective gas flow ratio is 1:5 to 1:1.5.

[0077] When the gas flow ratio of the gaseous carbon source to the protective gas is within the above range, the silicon-carbon composite material has excellent processing efficiency and a suitable specific surface area. This avoids the problem of long coating time and slow production efficiency caused by an excessively low gas flow ratio, while also avoiding the problem of excessively high gas flow ratio causing the gaseous carbon source to decompose too quickly and easily accumulate locally on the surface of secondary particles, making it impossible to form a uniform amorphous carbon coating layer and effectively reduce the specific surface area of ​​the silicon-carbon composite material.

[0078] In any embodiment, the binder includes at least one of phenolic resin, styrene-butadiene rubber, polyacrylic acid, carboxymethyl cellulose, sodium alginate, carboxymethyl polysaccharide, polyacrylonitrile, and polyacryl alcohol.

[0079] The aforementioned binder can provide adhesion between silicon-containing material particles and carbon-based material particles. In addition, it will shrink due to heat during the second spray granulation step to form pores and retain functional groups that play a bonding role and remove volatiles during the carbonization step. This gives the silicon-carbon composite material a certain porosity, leaving space for the expansion of silicon-containing material particles and improving the battery's storage performance and cycle stability.

[0080] A third aspect of this application provides a secondary battery, including a negative electrode sheet, wherein the negative electrode sheet comprises a silicon-carbon composite material of the first aspect or a silicon-carbon composite material prepared by the preparation method of the second aspect.

[0081] The fourth aspect of this application also provides an electrical device, including the secondary battery of the third aspect. Attached Figure Description

[0082] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0083] Figure 2 yes Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown.

[0084] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0085] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0086] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown;

[0087] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0088] Explanation of reference numerals in the attached figures:

[0089] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0090] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the silicon-carbon composite material, its preparation method, secondary battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0091] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0092] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0093] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0094] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0095] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0096] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0097] With the increasing application of rechargeable batteries, the requirements for their performance, such as energy density, are gradually increasing. The negative electrode active material has a significant impact on the energy density of rechargeable batteries. Silicon-carbon composite materials, as a novel type of negative electrode material, can effectively improve battery energy density and have been extensively studied. However, in traditional silicon-carbon composite materials, silicon-containing materials and carbon-based materials are usually in a uniformly distributed or directly mixed state. This means that the part of the silicon-carbon composite material in contact with the electrolyte also contains silicon, leading to continuous reactions between silicon and the electrolyte, consuming active ions, and deteriorating the battery's storage and cycle performance.

[0098] [Silicon-carbon composite materials]

[0099] Based on this, this application provides a silicon-carbon composite material, which includes an internal region and an external region. The internal region is mainly composed of silicon-containing material particles, and the external region is mainly composed of carbon-based material particles.

[0100] In some embodiments, the silicon-containing material particles include at least one of elemental silicon, silicon-oxygen materials, silicon-carbon materials, and silicon-metal alloys.

[0101] In some embodiments, the silicon-containing material particles include silicon-carbon materials.

[0102] In some embodiments, the carbon-based material particles include at least one of artificial graphite and natural graphite.

[0103] In some embodiments, the carbon-based material particles include artificial graphite.

[0104] In this article, the term "silicon-carbon composite material" refers to a composite material composed of two elements: silicon and carbon.

[0105] Silicon has a higher specific capacity than carbon-based materials, but its high surface reactivity makes it prone to electrolyte decomposition on the silicon anode surface, leading to a decline in its storage performance. Furthermore, the lithium storage mechanism of silicon anodes dictates significant volume expansion and contraction during lithium insertion / extraction, which not only deteriorates battery cycle performance but also causes continuous cracking and formation of the solid electrolyte interphase (SEI) film, continuously consuming active ions and further worsening battery storage performance. While carbon-based materials have lower surface activity and structural stability compared to silicon, they cannot further improve battery energy density. Therefore, the silicon-carbon composite material provided in this application is a secondary particle structure where the internal region is mainly composed of silicon-containing material particles and the external region is mainly composed of carbon-based material particles. This structure enables the battery to achieve excellent energy density while simultaneously improving battery storage performance by reducing the surface activity of the silicon-carbon composite material and isolating silicon from the electrolyte. Additionally, the high strength of the carbon-based material particles in the external region inhibits the volume expansion of the silicon-containing material particles, enhancing the structural stability of the silicon-carbon composite material and further improving the battery's cycle stability.

[0106] Compared to silicon-carbon composite materials that directly mix silicon-containing material particles with carbon-based material particles or are secondary particles that are uniformly distributed, the silicon-carbon composite material of this application can not only isolate silicon from the electrolyte, but also reserve space for the volume expansion of silicon-containing material particles by leaving gaps, thereby improving the battery's storage performance and cycle stability, while also taking into account excellent energy density.

[0107] In some implementations, the number of silicon-containing material particles in the internal region is less than or equal to 3, and can be selected as 1-2.

[0108] The number of silicon-containing material particles in the internal region can be tested using methods known in the art. As an example, an argon ion beam is used to cut the silicon-carbon composite material perpendicular to its surface to expose the cross-section. The cross-section is then photographed using a scanning electron microscope to observe the number of silicon-containing material particles in the internal region.

[0109] In some implementations, the number of silicon-containing material particles in the internal region is 1, 2, or 3.

[0110] When the number of silicon-containing material particles in the internal region is within the above range, it is beneficial for the carbon-based material particles to densely encapsulate the silicon-containing material particles, and to control the particle size of the finished silicon-carbon composite material within a suitable range. This reduces the contact between silicon and electrolyte, improves the dynamic performance of the battery, and also meets the processing performance requirements of silicon-carbon composite materials during negative electrode slurry homogenization and negative electrode coating, so that the battery can take into account excellent storage performance, cycle stability and dynamic performance.

[0111] In some embodiments, the mass percentage of silicon in the region r / 2 from the geometric center of the silicon-carbon composite material is greater than or equal to 30%, and can be selected as 35%-45%, where r represents the minor axis of the silicon-carbon composite material.

[0112] In some embodiments, the carbon content in the region extending inward from the outer surface of the silicon-carbon composite material by a distance of r / 2 is greater than or equal to 80%, and can be selected as 90%-100%, where r represents the minor diameter of the silicon-carbon composite material.

[0113] The minor diameter of silicon-carbon composite materials can be determined using a triaxial characterization method, as follows: the minor diameter r is measured on a planar projection diagram of the negative electrode material.

[0114] The mass percentage of silicon in the region r / 2 from the geometric center of the silicon-carbon composite material, and the mass percentage of carbon in the region extending r / 2 from the outer surface inward, can be tested using methods known in the art. As an example, ion-polished cross-sectional elemental analysis (CP) is used, tested according to the GB-T17359-2012 standard. Based on the CP elemental spectrum of a single particle, the distribution positions of Si and C elements can be determined. The content of silicon and carbon elements in the range from the geometric center to 1 / 2r can be directly tested in the corresponding regions of the particle. The calculation method for the carbon content in the range from 1 / 2r to r is as follows: Let the carbon content of the entire particle obtained from the CP elemental analysis be A, the carbon content in the range from the center to 1 / 2r be B, and the carbon content in the range from 1 / 2r to r be C.

[0115]

[0116] In some embodiments, the mass percentage of silicon in the region r / 2 from the geometric center of the silicon-carbon composite material is 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, or any value between the two.

[0117] When the mass percentage of silicon in the region r / 2 from the geometric center of the silicon-carbon composite material is within the above range, the battery can achieve excellent energy density, storage performance, and cycle stability.

[0118] In some embodiments, the mass percentage of carbon in the region extending inward from the outer surface of the silicon-carbon composite material by a distance r / 2 is 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, 98%, 100%, or any value between two of these.

[0119] When the mass percentage of carbon element in the region extending from the outer surface of the silicon-carbon composite material to the inner surface at a distance of r / 2 is within the above range, the silicon-carbon composite material can isolate silicon from the electrolyte, suppress the volume change of silicon during the lithium insertion / extraction process, and improve the storage performance and cycle stability of the battery.

[0120] In some embodiments, the outer region of the silicon-carbon composite material further includes an amorphous carbon coating layer.

[0121] In this paper, the term "amorphous carbon" refers to an amorphous structure composed of carbon elements. Its hybrid sp3 and sp2 hybrid structure makes it different from crystalline carbon in crystalline systems, and it has a structure and properties similar to amorphous objects (such as glass).

[0122] The amorphous carbon described herein can be formed by carbonization of a gaseous carbon source. The gaseous carbon source can be a gas known in the art suitable for coating, such as at least one of methane, ethylene, and acetylene.

[0123] The amorphous carbon coating layer in the outer region can further isolate the silicon from the electrolyte and reduce the specific surface area of ​​the silicon-carbon composite material. This avoids the secondary particles from having an uneven surface, which would lead to an excessively large specific surface area of ​​the silicon-carbon composite material, increase the contact area with the electrolyte, and reduce the amount of active ions consumed in the formation of the SEI film. As a result, the battery's storage performance, cycle stability, and first-time efficiency are comprehensively improved.

[0124] In some embodiments, the Dv50 of the silicon-containing material particles is greater than or equal to the Dv50 of the carbon-based material particles.

[0125] In this paper, the terms "Dv50", "Dv90", and "Dv10" refer to the particle size corresponding to the cumulative volume distribution number of particles reaching 50%, 90%, and 10% in the particle size distribution curve.

[0126] In this application, Dv50, Dv90, and Dv10 can be tested using methods known in the art. As an example, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, weigh 0.1g to 0.13g of sample into a 50mL beaker, then weigh 5g of anhydrous ethanol and add it to the beaker containing the sample. Place a stir bar approximately 2.5mm in length inside and seal with plastic wrap. Place the sample in an ultrasonic machine and sonicate for 5 minutes. Transfer to a magnetic stirrer and stir at 500r / min for at least 20 minutes. Two samples are randomly selected from each batch of product for testing, and the particle size distribution is measured to obtain the sample's Dv50, Dv90, and Dv10. These values ​​can be conveniently determined using a laser particle size analyzer, such as the Malvern Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0127] The Dv50 of silicon-containing material particles is greater than or equal to that of carbon-based material particles, which helps to improve the integrity of the silicon-containing material particles coated by carbon-based material particles, thereby improving the storage performance of the battery.

[0128] In some embodiments, the Dv50 of the silicon-containing material particles is less than or equal to 5 μm.

[0129] In some embodiments, the Dv50 of the silicon-containing material particles is a value range of 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any two of these values.

[0130] When the Dv50 of silicon-containing material particles is within the above range, it is beneficial to control the particle size of the finished silicon-carbon composite material within a suitable range, which results in good electrode processing performance and kinetic performance.

[0131] In some embodiments, the Dv50 of the carbon-based material particles is less than or equal to 5 μm.

[0132] In some embodiments, the Dv50 of the carbon-based material particles is a value range of 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, or any two of these values.

[0133] When the particle size of carbon-based material particles is within the above range, the integrity of the carbon-based material particles coating the silicon-containing material particles can be improved, and it is also beneficial to control the particle size of the finished silicon-carbon composite material within a suitable range, so as to meet the performance requirements of electrode processing and improve the storage performance and dynamic performance of the battery.

[0134] In some embodiments, the silicon-containing material particles comprise a carbon substrate with a porous structure and a silicon-based material disposed within the porous structure of the carbon substrate.

[0135] The porous structure of the carbon substrate provides attachment sites for silicon-based materials, enabling large-scale silicon storage. Silicon-based materials uniformly dispersed within the porous structure of the carbon substrate are less prone to agglomeration. Furthermore, the carbon substrate mitigates the volume changes of silicon-based materials within the porous structure during lithium insertion / extraction and can withstand the stress caused by these volume changes. This results in silicon-containing material particles exhibiting low expansion rates and high stability, improving their capacity, storage performance, and cycle stability. The internal region of the silicon-carbon composite material contains silicon-containing material particles with the aforementioned structure, which not only increases battery capacity but also prevents cracking during cycling due to excessive internal volume expansion, thereby enhancing the battery's storage performance and cycle stability.

[0136] In some embodiments, the carbon substrate includes micropores with a pore size of less than 2 nm, mesopores with a pore size of 2 nm to 50 nm, and macropores with a pore size of greater than 50 nm.

[0137] The pore structure of carbon substrates can be tested using equipment and methods known in the art. For example, the pore size can be tested using the gas adsorption method, according to the test standards GB / T19587-2017 & GB / T21650.2-2008. Specifically, the porous material sample tube is immersed in liquid nitrogen at -196℃, and nitrogen gas is adsorbed onto the material under the relative pressure of 0-1. The pore size distribution of the porous material is characterized based on the relationship between the volume of each pore size and the corresponding partial pressure. The pore size distribution is used to characterize the pore structure of the carbon substrate.

[0138] The aforementioned porous structure in the carbon substrate facilitates the adhesion of silicon-based materials within the porous structure and effectively limits the volume expansion of the silicon-based materials attached to the porous structure. Moreover, the expanded silicon-based materials do not cause significant damage to the porous structure of the carbon substrate, thereby increasing the particle capacity of silicon-containing materials while ensuring structural stability.

[0139] In some embodiments, the pore volume of the micropores is greater than or equal to 0.5 cm³. 3 / g, can be selected as 0.6cm 3 / g-0.9cm 3 / g.

[0140] The pore volume of micropores can be determined using instruments and methods known in the art. For example, the test method can refer to GB / T19587-2004, using the mesopore size distribution test BJH (Barret joyner Halenda), and using the gas adsorption-desorption method under the micro-mesopore model to test and select adsorption branch data, and measure and count the total pore volume of pores with a pore size of less than 2 nm.

[0141] In some embodiments, the pore volume of the micropore is 0.5 cm³. 3 / g, 0.55cm 3 / g, 0.6cm 3 / g, 0.65cm 3 / g, 0.7cm 3 / g, 0.75cm 3 / g, 0.8cm 3 / g, 0.85cm 3 / g, 0.9cm 3 / g, 0.95cm 3 / g, 1cm 3 / g or any value between the two.

[0142] By controlling the pore volume of micropores in carbon substrates, it is beneficial for silicon-containing precursors to enter the pore structure of carbon substrates, reducing the risk of silicon deposition on the surface of carbon substrates and improving the specific capacity and storage performance of silicon-containing material particles.

[0143] In some embodiments, the average pore size of the carbon substrate is less than or equal to 5 nm, and can be selected as 1 nm to 3.5 nm.

[0144] The average pore size of carbon substrates can be tested using equipment and methods known in the art. For example, the pore size can be tested using the gas adsorption method, according to the test standards GB / T19587-2017 & GB / T21650.2-2008, as follows: The porous material sample tube is immersed in liquid nitrogen at -196℃, and nitrogen gas is adsorbed onto the material under the relative pressure of 0-1. The pore size distribution of the porous material is characterized based on the relationship between the volume of each pore size and the corresponding partial pressure, and the average pore size of the carbon substrate is obtained.

[0145] In some embodiments, the average pore size of the carbon substrate is 1 nm, 1.5 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, or any value between two of these.

[0146] When the average pore size of the carbon substrate is within the above range, it helps the silicon-based material to adhere, and the carbon substrate can limit the volume expansion of the silicon-based material in the pores. The expanded silicon-based material will not cause damage to the porous carbon matrix structure, thereby improving the capacity and structural stability of the silicon-containing material particles, and the battery has excellent storage performance and cycle stability.

[0147] In some embodiments, the specific surface area of ​​the carbon substrate is greater than or equal to 1200 m². 2 / g, optional 1500m 2 / g-1800m 2 / g.

[0148] In this application, the specific surface area of ​​the carbon substrate can be tested using methods known in the art. As an example, the specific surface area is tested using the gas adsorption method, according to the GB / T19587-2017 testing standard, specifically as follows: The sample tube is immersed in liquid nitrogen at -196℃, and the amount of nitrogen adsorbed on the solid surface at different pressures (0.05-0.30) is measured. Based on the BET multilayer adsorption theory and its formula, the monolayer adsorption amount of the sample is calculated, thereby determining the specific surface area of ​​the solid.

[0149]

[0150] Where n a The amount of adsorbed gas is expressed in mol / g; p / p0 is the relative pressure; n m This represents the monolayer adsorption capacity.

[0151] In some embodiments, the specific surface area of ​​the carbon substrate is 1200 m². 2 / g、1300m 2 / g, 1400m 2 / g, 1500m 2 / g, 1600m 2 / g、1700m 2 / g、1800m 2 / g or any value between the two.

[0152] The carbon substrate has a specific surface area within the above range. The carbon substrate has excellent pore volume, providing more deposition sites for silicon-based materials, which is beneficial to improving the specific capacity of silicon-containing material particles.

[0153] In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon-oxygen materials, silicon-carbon materials, and silicon-metal alloys.

[0154] In some embodiments, the silicon-based material comprises silicon grains.

[0155] The crystal structure of silicon-based materials can be tested using equipment and methods known in the art. As an example, the following steps can be taken: Select a microgrid of a certain diameter (e.g., 3 mm), hold the edge of the microgrid with pointed tweezers, and gently place it flat on white filter paper with the film side facing upwards (the side that appears glossy under light). Take an appropriate amount of sample (e.g., 1 g) and add it to a beaker containing an appropriate amount of ethanol, and sonicate for 10-30 minutes. Use a glass capillary tube to aspirate the sample and then drop 2-3 drops of the sample onto the microgrid. After baking in an oven for 5 minutes, place the microgrid with the sample onto the sample stage and test it using a transmission electron microscope (e.g., Hitachi HF-3300S Cs-corrected STEM) at a certain magnification (e.g., 60,000x) to obtain a transmission electron microscope (TEM) image of the sample. If there are obvious lattice fringes (for example, the fringe spacing is about 0.331 nm), it is crystalline silicon; if no lattice fringes are observed, it is amorphous silicon.

[0156] In this application, the size of the silicon grains can be determined by testing the XRD pattern of the sample according to the JIS / K0131-1996 testing standard. Based on the XRD pattern of the sample, the full width at half maximum (FWHM) β and the diffraction angle θ of the Si(111) crystal plane diffraction peak are taken and substituted into the Debye-Scherrer formula to calculate the grain size of the silicon grains. The Debye-Scherrer formula is as follows: Dhkl=kλ / (βcosθ), where Dhkl represents the grain size of the silicon grains in nm; k represents the Scherrer constant, 0.89; λ represents the incident X-ray wavelength, 0.15406 nm; β represents the FWHM of the diffraction peak in rad; and θ represents the diffraction angle in degrees.

[0157] In some embodiments, the size of the silicon grain is less than or equal to 10 nm, and optionally, the size of the silicon grain is less than or equal to 3 nm.

[0158] In some embodiments, the size of the silicon grain is 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any value between two of these.

[0159] By keeping the size of silicon grains within the above range, it is possible to avoid excessive local enrichment of silicon elements due to excessively large grain size, which could cause the silicon-containing material particles to expand significantly during lithium intercalation and lead to cracking. This is beneficial for improving the storage performance and cycle stability of the battery.

[0160] In some implementations, the silicon-based material includes amorphous silicon.

[0161] Amorphous silicon can expand uniformly in all directions, thereby causing uniform compression of the carbon substrate. The carbon substrate can effectively alleviate the volume expansion of amorphous silicon, thus improving the storage performance and cycle stability of the battery.

[0162] In some embodiments, the carbon substrate includes at least one of graphite, soft carbon, and hard carbon.

[0163] In some embodiments, the carbon substrate is hard carbon.

[0164] In some embodiments, the pore volume of the hard carbon micropores is greater than or equal to 0.5 cm³. 3 / g, can be selected as 0.6cm 3 / g-0.9cm 3 / g. In some embodiments, the specific surface area of ​​hard carbon is greater than or equal to 1200 m². 2 / g, optional 1500m 2 / g-1800m 2 / g. In some embodiments, the average pore size of the hard carbon is less than or equal to 5 nm, optionally 1 nm to 3.5 nm.

[0165] When the micropore volume, specific surface area, and average pore size of hard carbon are within the above range, hard carbon and silicon-based materials deposited in the pore structure work together to improve the specific capacity and structural stability of silicon-containing material particles.

[0166] In some embodiments, based on the total mass of the silicon-containing material particles, the mass percentage of silicon in the silicon-containing material particles is 35%-50%, optionally 35%-47%.

[0167] In some embodiments, based on the total mass of the silicon-containing material particles, the mass percentage of silicon in the silicon-containing material particles is 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or any value between these values.

[0168] Based on the total mass of the silicon-containing material particles, the mass percentage of silicon in the silicon-containing material particles is within the above-mentioned range, which is beneficial to improving the specific capacity and structural stability of silicon-carbon composite materials, and improving the cycle stability and storage performance of batteries.

[0169] In some embodiments, the porosity of the silicon-carbon composite material is 20%-45%, optionally 20%-35%.

[0170] In this application, the porosity of the silicon-carbon composite material can be tested using methods known in the art. As an example, the test is conducted according to the GB / T24586 test standard, with porosity P = (V2 - V1) / V2 * 100% and apparent volume V2 = S * H ​​* A, where S is the area in cm². 2 H represents thickness in cm; A represents the number of samples in EA; V1 represents the true volume of the sample in cm³. 3 V2 is the apparent volume of the sample, in cm³. 3 ;

[0171] The true volume V1 of the sample is calculated as follows: The sample is placed in a true density analyzer (Accu Pyc II1340 analyzer), the test system is sealed, and helium gas is introduced according to the program. By detecting the gas pressure in the sample chamber and the expansion chamber, and then according to the ideal gas law (v = nRT / P), the gas volumes in the sample chamber and the expansion chamber are obtained respectively. Thus, the volume of gas displaced by the sample under certain temperature and pressure conditions is obtained, which is the true volume V1 of the sample.

[0172] In some embodiments, the porosity of the silicon-carbon composite material is 20%, 25%, 30%, 35%, 40%, 45%, or any value between two of these.

[0173] The porosity of the silicon-carbon composite material is within the above range, which leaves room for the volume change that occurs when silicon-based material particles in the internal region are inserted or extracted with lithium. While taking into account the excellent specific capacity, it can also improve the structural stability of the silicon-carbon composite material, thereby improving the energy density, storage performance and cycle stability of the battery.

[0174] In some embodiments, the Dv50 of the silicon-carbon composite material is less than or equal to 16 μm, and can be selected as 8 μm-16 μm.

[0175] In some embodiments, the Dv50 of the silicon-carbon composite material is a range of 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm or any combination thereof.

[0176] When the Dv50 of silicon-carbon composite materials is within the above range, the materials have excellent kinetic properties and electrode processing properties, which are beneficial to improving the storage performance and cycle stability of batteries.

[0177] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the silicon-carbon composite material is 0.5-1.8, and optionally 0.8-1.5.

[0178] In some embodiments, the particle size distribution (Dv90-Dv10) / Dv50 of the silicon-carbon composite material is a range of 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8 or any two of these values.

[0179] When the particle size distribution of silicon-carbon composite materials is within the above range, the overall average particle size of the silicon-carbon composite material is relatively moderate and the particle size distribution is relatively uniform, which is beneficial to improving the uniformity of the overall performance of silicon-carbon composite materials.

[0180] In some embodiments, the powder compaction density of the silicon-carbon composite material at 49000 N is 0.7 g / cm³. 3 -1.3g / cm 3 0.95g / cm³ is an optional value. 3 -1.1g / cm 3

[0181] In this article, the term "powder compaction density" refers to the mass of powder particles per unit volume under a given pressure.

[0182] In this application, the compacted density of silicon-carbon composite material powder under 49000N pressure can be tested using methods known in the art. As an example, referring to GB / T24533-2009, 1g of silicon-carbon composite material powder is weighed and added to a container with a bottom area of ​​1.327cm². 2 In the mold, the pressure is increased to 5000 kg (equivalent to 49000 N), held for 30 seconds, then depressurized and held for 10 seconds. The compaction density of the silicon-carbon composite material under 49000 N pressure is determined by an electronic pressure testing machine (such as UTM7305 electronic pressure testing machine).

[0183] In some embodiments, the powder compaction density of the silicon-carbon composite material at 49000 N is 0.7 g / cm³. 3 0.8g / cm 3 0.9g / cm 3 1.0g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 Or the range of values ​​between any two.

[0184] When the powder compaction density of silicon-carbon composite materials is within the above-mentioned range, the negative electrode sheet has a higher compaction density, which further improves the energy density of the battery. In addition, the negative electrode film layer has a strong ability to maintain the pore structure during cycling, and the electrolyte wettability of the negative electrode sheet is better, which is beneficial to improving the battery's storage performance and cycle stability.

[0185] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is less than or equal to 6 m². 2 / g, can be less than or equal to 4.5m 2 / g.

[0186] In some embodiments, the specific surface area of ​​the silicon-carbon composite material is 1 m². 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g or any value between the two.

[0187] When the specific surface area of ​​the silicon-carbon composite material is within the above range, it helps to further reduce the contact area between the silicon-carbon composite material and the electrolyte, reduce the consumption of active ions by the formation of the SEI film, and improve the battery's initial efficiency, storage performance and cycle stability.

[0188] This application also provides a method for preparing a silicon-carbon composite material, comprising the following steps: providing silicon-containing material particles and carbon-based material particles; performing a first spray granulation on the silicon-containing material particles and a binder to obtain a first intermediate product; spraying the carbon-based material particles onto the surface of the first intermediate product to perform a second spray granulation to obtain the silicon-carbon composite material; the silicon-carbon composite material includes an internal region and an external region, wherein the internal region is mainly composed of silicon-containing material particles and the external region is mainly composed of carbon-based material particles.

[0189] In this paper, "spray granulation" refers to a granulation method in which a slurry or solution is sprayed into a granulation tower, where it dries and agglomerates under the action of hot spray air, thereby obtaining spherical agglomerates. This method is widely used to produce catalysts of various particle sizes or other particles with specific particle size requirements. It is suitable for both experimental and small-scale production, producing high-precision and uniform granules.

[0190] The silicon-containing material particles and binder are first spray-granulated to control the particle size of the silicon-containing material particles in the internal region of the silicon-carbon composite material, resulting in a first intermediate product in which the silicon-containing material particles are uniformly coated with the binder. By second spray-granulating carbon-based material particles onto the surface of the first intermediate product, secondary particles are obtained, consisting mainly of silicon-containing material particles internally and carbon-based material particles externally, with the carbon-based material particles tightly coating the silicon-containing material particles. Compared to methods that simultaneously mix and granulate silicon-containing material particles, binder, and carbon-based material particles, this two-step granulation method achieves a state where the silicon-containing material particles are completely coated with carbon-based material particles, isolating silicon from contact with the electrolyte, and allowing for the control of the porosity of the silicon-carbon composite material, thereby improving the battery's storage performance and cycle stability.

[0191] In some embodiments, the silicon-containing material particles are prepared by the following steps: providing a gas containing a silicon precursor to a carbon substrate having a porous structure; and generating a silicon-based material attached to the porous structure from the silicon precursor by chemical vapor deposition to obtain the silicon-containing material particles.

[0192] In some embodiments, the silicon precursor includes at least one of silane, dichlorosilane, trichlorosilane, and tetrachlorosilane.

[0193] In some implementations, the silicon precursor is silane.

[0194] In some embodiments, the mass ratio of the silicon-containing material particles to the binder is 1:2 to 2:1.

[0195] In some embodiments, the mass ratio of the silicon-containing material particles to the binder is 1:2, 1.5:2, 1:1, 1.5:1, 2:1, or any range between the two.

[0196] When the mass ratio of silicon-containing material particles to binder is within the above range, there is a good bonding effect between the silicon-containing material particles and the carbon-based material particles. When the particle size of the finished silicon-carbon composite material is within a suitable range, the battery has good storage performance and cycle stability while also having excellent energy density.

[0197] In some embodiments, the mass ratio of the silicon-containing material particles to the carbon-based material particles is 1:12 to 1:6.

[0198] In some embodiments, the mass ratio of the silicon-containing material particles to the carbon-based material particles is 1:12, 1:11, 1:10, 1:9, 1:8, 1:7, 1:6, or any range between the two.

[0199] When the mass ratio of silicon-containing material particles to carbon-based material particles is within the above range, the carbon-based material particles form a complete coating layer on the surface of the silicon-containing material particles, isolating silicon from contact with the electrolyte. Furthermore, the silicon-carbon composite material will not reduce its specific capacity due to excessive coating caused by an excessive proportion of carbon-based material particles. As a result, the battery has excellent energy density, storage performance, and cycle stability.

[0200] In some embodiments, the temperature difference between the inlet and outlet air temperatures of the first spray granulation is no greater than 60°C.

[0201] In some embodiments, the temperature difference between the inlet and outlet air temperatures of the first spray granulation is 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, or any value between the two.

[0202] Spray granulation relies on hot air to dry materials, and the drying state of the intermediate product is controlled by adjusting the temperature of the hot air. Because the temperature of hot air drying is greatly affected by the environment, and the chamber only provides insulation without heating, the temperature inside the chamber is not an exact temperature, but rather a temperature range. Setting the difference between the inlet and outlet air temperatures within this range ensures that the chamber temperature remains within a suitable range, preventing the actual temperature inside the chamber from being too low due to an excessively large temperature difference.

[0203] In some implementations, the inlet air temperature is 110°C-150°C.

[0204] In some implementations, the inlet air temperature is 110°C, 120°C, 130°C, 140°C, 150°C, or any value between two of these.

[0205] The inlet air temperature is the initial heat source in the chamber. Spray granulation relies on the inlet air to dry the material, ensuring that the silicon-containing material particles coated with the binder are in a semi-dry state. This prevents the silicon-containing material particles from sticking together due to excessively low temperature and moisture, which would result in larger silicon-containing material particle sizes in the internal regions of the finished silicon-carbon composite material, leading to an overall larger particle size in the finished product. Alternatively, excessively high temperature and dryness would prevent the next process from proceeding. Within the aforementioned inlet air temperature range, the silicon-carbon composite material exhibits good kinetic properties and electrode processing performance.

[0206] In some implementations, the outlet air temperature is 50°C-90°C.

[0207] In some implementations, the outlet air temperature is 50°C, 60°C, 70°C, 80°C, 90°C, or any range between two of these.

[0208] The outlet air temperature is the result of comprehensive consideration of heat, and is determined by factors such as the inlet air temperature and the feeding rate. Setting the outlet air temperature of the first spray granulation within this range can avoid the temperature difference between the outlet air temperature and the inlet air temperature being too large, which would cause the temperature inside the chamber to be too low. It can also further ensure that the first intermediate product is in a semi-dry state, which is beneficial for it to proceed to the next process.

[0209] In some embodiments, the feed air pressure for the first spray granulation is 250 kPa-350 kPa, and optionally 280 kPa-320 kPa.

[0210] In some embodiments, the feed air pressure for the first spray granulation is 250 kPa.

[0211] 251 kPa, 252 kPa, 253 kPa, 254 kPa, 255 kPa, 256 kPa, 257 kPa, 258 kPa, 259 kPa, 260 kPa, or any range of two.

[0212] The feed air pressure in the first spray granulation is a crucial step in controlling the particle size of the finished silicon-carbon composite material. When the feed air pressure is within the aforementioned range, the number and size of the sprayed silicon-containing material particles can be controlled within a suitable range. This avoids excessively large particle sizes due to low air pressure, which would lead to an overly large finished silicon-carbon composite material particle size, deteriorating the kinetic properties and electrode processing performance of the silicon-carbon composite material. It also avoids situations where excessively high air pressure causes some silicon-containing material particles to become stuck at the spray nozzle and fail to be sprayed. When the feed air pressure in the first spray granulation is within the aforementioned range, the particle size of the sprayed silicon-containing material is kept within a suitable range, ensuring that the number of silicon-containing material particles in the internal region of the silicon-carbon composite material does not exceed three. This is beneficial for improving the storage performance and electrode processing performance of the silicon-carbon composite material.

[0213] In some embodiments, the temperature difference between the inlet and outlet air temperatures of the second spray granulation is 20°C-40°C.

[0214] In some embodiments, the temperature difference between the inlet and outlet air temperatures of the second spray granulation is 20°C, 24°C, 28°C, 32°C, 36°C, 40°C, or any value between the two.

[0215] In some embodiments, the inlet air temperature for the second spray granulation is 170°C-280°C.

[0216] In some embodiments, the inlet air temperature of the second spray granulation is 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, or any value between two of these.

[0217] The inlet air temperature in the second spray granulation step is crucial for controlling the strength and structural stability of the silicon-carbon composite material. Because the first intermediate product has a certain viscosity, it needs to be rapidly coated with carbon-based material particles to form secondary particles and then dried. This prevents the first intermediate product and secondary particles from agglomerating or undergoing secondary bonding due to excessively low temperatures; it also prevents the binder from shrinking too quickly or failing due to excessively high temperatures, thus failing to achieve a good bonding effect. When the inlet air temperature of the second spray granulation is within this range, the prepared silicon-carbon composite material exhibits suitable particle size, excellent strength, and structural stability, playing a role in consistently improving storage performance and cycle performance throughout the battery's lifespan.

[0218] In some embodiments, the outlet air temperature of the second spray granulation is 130°C-240°C.

[0219] In some embodiments, the outlet air temperature of the second spray granulation is 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, or any value between two of these.

[0220] In some embodiments, the feed air pressure for the second spray granulation is 150 kPa-260 kPa, and optionally 180 kPa-210 kPa.

[0221] In some embodiments, the feed pressure of the second spray granulation is 150 kPa, 160 kPa, 170 kPa, 180 kPa, 190 kPa, 200 kPa, 210 kPa, 220 kPa, 230 kPa, 240 kPa, 250 kPa, 260 kPa, or any value between two of these.

[0222] The feed pressure in the second spray granulation process is a crucial step in controlling the integrity and uniformity of the silicon-containing material particles coated by the carbon-based material particles. Maintaining the feed pressure within the aforementioned range can improve the battery's storage performance and cycle stability. It avoids situations where excessive pressure and feed rate lead to an excessive number of carbon-based material particles coating the silicon-carbon composite material, resulting in a larger particle size and thus deteriorating the kinetic properties, electrode processing performance, and specific capacity of the silicon-carbon composite material. Conversely, it avoids situations where insufficient pressure and feed rate result in some silicon-containing material particles not being completely coated by the carbon-based material particles, failing to completely isolate silicon from the electrolyte, and weakening the storage performance of the silicon-carbon composite material.

[0223] In some embodiments, the method for preparing the silicon-carbon composite material further includes: introducing a gaseous carbon source after the second spray granulation, followed by gas phase coating and carbonization to obtain the silicon-carbon composite material.

[0224] The secondary particles formed by carbon-based material particles coating silicon-containing material particles have more uneven surfaces and a larger specific surface area. After carbon coating, the specific surface area of ​​silicon-carbon composite materials can be controlled within a suitable range, enabling the battery to have excellent storage performance, cycle stability and first-time efficiency. In addition, the carbon coating layer in the outer region can further reduce the possibility of silicon contacting the electrolyte, further improving the battery's storage performance.

[0225] In some embodiments, the gaseous carbon source includes gaseous hydrocarbons, which may be at least one of methane, ethylene, and acetylene.

[0226] In some embodiments, the gaseous carbon source is acetylene.

[0227] The temperature at which the aforementioned gaseous carbon source decomposes to form the carbon coating layer is within a suitable range, satisfying the temperature requirements of each component of the silicon-carbon composite material.

[0228] In some embodiments, the carbonization temperature is 400°C-800°C.

[0229] In some embodiments, the carbonization temperature is 400°C, 500°C, 600°C, 700°C, 800°C, or any value between two of these.

[0230] When the carbonization temperature is within the above range, the gaseous carbon source can decompose to produce carbides that coat the surface of the secondary particles, forming a carbon coating layer. This reduces the specific surface area of ​​the secondary particles and further isolates the silicon from the electrolyte, improving the battery's storage performance and cycle stability. It also avoids the formation of silicon carbide from silicon-containing material particles due to excessively high temperatures, thus achieving the goal of not losing the specific capacity of the silicon-carbon composite material.

[0231] In some embodiments, the carbonization time is 0.2h-2h.

[0232] In some embodiments, the carbonization time is 0.2h, 0.3h, 0.4h, 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, 1h, 1.1h, 1.2h, 1.3h, 1.4h, 1.5h, 1.6h, 1.7h, 1.8h, 1.9h, 2h, or any value between two of these.

[0233] When the carbonization time is within the above range, the silicon-carbon composite material has a suitable specific surface area and excellent capacity. This avoids the problem of insufficient amorphous carbon coating due to too short a time, which would prevent the secondary particle surface from being completely covered and thus reduce the specific surface area. It also avoids the risk of silicon forming silicon carbide due to excessively long carbonization time, which would cause a loss of capacity in the silicon-carbon composite material.

[0234] In some embodiments, the protective gas during the carbonization process is nitrogen or argon. Optionally, the gaseous carbon source to the protective gas flow ratio is 1:5 to 1:1.5.

[0235] In some embodiments, the gaseous carbon source to the protective gas flow ratio is 1:5, 1:4.5, 1:4, 1:3.5, 1:3, 1:2.5, 1:2, 1:1.5 or any range between the two.

[0236] When the gas flow ratio of the gaseous carbon source to the protective gas is within the above range, the silicon-carbon composite material has excellent processing efficiency and a suitable specific surface area. This avoids the problem of long coating time and slow production efficiency caused by an excessively low gas flow ratio, while also avoiding the problem of excessively high gas flow ratio causing the gaseous carbon source to decompose too quickly and easily accumulate locally on the surface of secondary particles, making it impossible to form a uniform amorphous carbon coating layer and effectively reduce the specific surface area of ​​the silicon-carbon composite material.

[0237] In some embodiments, the binder includes at least one of phenolic resin, styrene-butadiene rubber, polyacrylic acid, carboxymethyl cellulose, sodium alginate, carboxymethyl polysaccharide, polyacrylonitrile, and polyacryl alcohol.

[0238] In some embodiments, the binder includes phenolic resin.

[0239] The aforementioned binder can provide adhesion between silicon-containing material particles and carbon-based material particles. In addition, it will shrink due to heat during the second spray granulation step to form pores and retain functional groups that play a bonding role and remove volatiles during the carbonization step. This gives the silicon-carbon composite material a certain porosity, leaving space for the expansion of silicon-containing material particles and improving the battery's storage performance and cycle stability.

[0240] [Negative electrode plate]

[0241] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. The negative electrode film layer includes a negative electrode active material, which includes silicon-carbon composite material in some embodiments or silicon-carbon composite material prepared by the preparation method in some embodiments.

[0242] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0243] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0244] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0245] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0246] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0247] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0248] [Positive electrode plate]

[0249] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0250] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0251] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0252] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0253] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0254] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0255] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0256] [Electrolytes]

[0257] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0258] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0259] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0260] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0261] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0262] [Isolation membrane]

[0263] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0264] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0265] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0266] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0267] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0268] In this application, the shape of the secondary battery includes, but is not limited to, cylindrical, square, or other arbitrary shapes. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0269] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0270] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0271] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0272] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0273] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0274] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0275] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0276] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0277] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0278] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0279] Example

[0280] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0281] I. Preparation Method

[0282] Preparation Example 1: Silicon-containing material particles 1

[0283] At 465°C, a gas containing silane (SiH4) was introduced into a porous hard carbon substrate, and vapor deposition was performed for 10 hours. Through chemical vapor deposition (CVD), silicon-based material was deposited in the porous structure of the hard carbon substrate from the silane. Then, using CVD again at 660°C with a carbon source gas and protective gas gas ratio of 1:2, vapor deposition was performed on the hard carbon substrate for 0.5 hours. A carbon layer, comprising 3% of the total mass of the hard carbon substrate and the deposited silicon-based material, was coated onto the outer surface of the hard carbon substrate. The gas source was acetylene gas. Silicon-containing material particles were obtained. The mass ratio of silicon in the silane to the hard carbon substrate was 1:1; the pore volume of the hard carbon substrate micropores was 0.8 cm³. 3 / g, with an average pore size of 3.2nm and a specific surface area of ​​1612m². 2 / g, the silicon-based material contains silicon grains with a particle size of 2.9nm; the Dv50 of silicon-containing material particle 1 is 4.2μm, and the silicon mass percentage is 46%.

[0284] Preparation Example 2: Silicon-containing material particles 2

[0285] A gas containing silane (SiH4) was introduced into a porous hard carbon substrate at 465°C, and vapor deposition was performed for 8 hours. Silicon-based material was deposited within the porous structure of the hard carbon substrate via chemical vapor deposition (CVD). Then, CVD was performed again at 660°C using a carbon source gas and protective gas with a gas flow ratio of 1:2, and vapor deposition was performed on the hard carbon substrate for 0.5 hours. A carbon layer, comprising 3% of the total mass of the hard carbon substrate and the deposited silicon-based material, was formed on the outer surface of the hard carbon particles. The gas source was acetylene gas. This yielded silicon-containing material particles 2. The mass ratio of silicon in the silane to the hard carbon substrate was 2:3; the pore volume of the hard carbon substrate micropores was 0.8 cm³. 3 / g, with an average pore size of 3.2nm and a specific surface area of ​​1612m². 2 / g, the silicon-based material contains silicon grains with a particle size of 2.9nm; the silicon mass percentage of silicon-containing material particles 2 is 36%.

[0286] Preparation Example 3: Silicon-containing material particles 3

[0287] A gas containing silane (SiH4) was introduced into a porous hard carbon substrate at 465°C and vapor-phase deposition was performed for 9 hours. Silicon-based material was deposited within the porous structure of the hard carbon substrate via chemical vapor deposition (CVD). Then, CVD was performed again at 660°C using a carbon source gas and protective gas with a gas flow ratio of 1:2 for 0.5 hours. This resulted in a carbon layer comprising 3% of the total mass of the hard carbon particles and the deposited silicon-based material, with acetylene gas as the gas source. Silicon-containing material particles were obtained. The mass ratio of silicon in the silane to the hard carbon substrate was 2:3; the pore volume of the hard carbon substrate micropores was 0.4 cm³. 3 / g, with an average pore size of 3.5nm and a specific surface area of ​​1408m². 2 / g, the silicon-based material contains silicon grains with a particle size of 3.0nm; the silicon content in silicon-containing material particles 3 is 35% by mass.

[0288] Example 1

[0289] 1) Preparation of silicon-carbon composite materials

[0290] Silicon-containing material particles 1 and phenolic resin are mixed at a mass ratio of 1:1.2 and placed in the feed chamber 1 of the spraying equipment. Under nitrogen protection, the air pressure of the feed chamber 1 is set to 300 kPa, the air inlet temperature is 130°C, and the air outlet temperature is 70°C to obtain the intermediate product, namely the first intermediate product of the semi-dry coating adhesive.

[0291] Graphite with a Dv50 of 3.8 μm and the intermediate product prepared above were placed in feed chamber 2. The mass ratio of graphite to silicon-containing material particles was 9:1. The air pressure in feed chamber 2 was set to 200 kPa, the inlet air temperature was 210°C, and the outlet air temperature was 170°C. Secondary particles were obtained, with the inner region mainly composed of silicon-containing material particles and the outer region mainly composed of graphite material particles.

[0292] The aforementioned secondary particles were placed in a heating chamber. Under a nitrogen atmosphere, the heating chamber was first heated to 660℃, and then a mixed gas of nitrogen and acetylene was introduced at a volume ratio of 1:2. The mixture was kept at this temperature for 0.5 hours, and carbon coating was applied to the surface of the secondary particles to obtain a silicon-carbon composite material. The silicon-carbon composite material exhibits the following characteristics: silicon content is 45% by mass in the region r / 2 from the geometric center; carbon content is 98% by mass in the region extending r / 2 from the outer surface to the inner surface; porosity is 28%; Dv50 is 13.1 μm; particle size distribution is 1.5; and the powder compaction density of the silicon-carbon composite material at 49000 N is 1.02 g / cm³. 3 Specific surface area is 4.3 m² 2 / g.

[0293] 2) Preparation of negative electrode sheet

[0294] The prepared silicon-carbon composite material, artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC-Na) thickener were thoroughly mixed in a deionized water solvent system at a weight ratio of 20:75:2:2:1 to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a 13 μm thick copper foil for the negative electrode current collector at a coating speed of 25 m / min and a coating oven temperature of 110 °C. Then, the negative electrode sheet was obtained by cold pressing and slitting.

[0295] 3) Preparation of positive electrode sheet

[0296] The positive electrode active material Li(Ni) 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a weight ratio of 96:2:2 to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto a 13 μm thick aluminum foil for the positive electrode current collector at a coating speed of 30 m / min. The coating oven temperature was 110 °C, and the positive electrode sheet was obtained after cold pressing and slitting.

[0297] 4) Preparation of electrolyte

[0298] In an argon-atmospheric glove box (H2O content <0.1ppm, O2 content <0.1ppm), lithium hexafluorophosphate (LiPF6) was dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio 3:7) and stirred until homogeneous to obtain an electrolyte with a lithium salt concentration of 1 mol / L. Then, fluoroethylene carbonate (FEC) was added, with the FEC content being 5% of the total electrolyte mass.

[0299] 5) Separating membrane

[0300] Polypropylene (PP) film is used as the separator.

[0301] 6) Battery manufacturing

[0302] The positive electrode, separator, and composite negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The electrode assembly is then wound up, tabs are welded on, and the assembly is placed in an outer package. Electrolyte is then injected and the package is sealed. After processes such as settling, cold pressing, formation, shaping, and capacity testing, the lithium-ion secondary battery prepared in Example 1 is obtained.

[0303] Example 2

[0304] The battery in Example 2 is prepared in a similar way to the battery in Example 1, except that it uses silicon-containing material particles 2, as shown in Table 1.

[0305] Examples 3-10

[0306] The batteries in Examples 3-10 are prepared in a similar manner to those in Example 1, except that the preparation parameters of the silicon-carbon composite material and / or the Dv50 of the graphite particles are adjusted, as shown in Table 1.

[0307] Example 11

[0308] The battery in Example 11 was prepared in a similar manner to the battery in Example 1, except that the Dv50 of the graphite particles was adjusted, as shown in Table 1.

[0309] Example 12

[0310] The battery in Example 12 is prepared in a similar way to the battery in Example 1, except that it uses silicon-containing material particles 3, as shown in Table 1.

[0311] Table 1

[0312]

[0313] Comparative Example 1

[0314] The battery in Comparative Example 1 is prepared using a similar method to the battery in Example 1, except that the silicon-carbon composite material is a secondary particle obtained by directly mixing and granulating silicon-containing material particles and graphite. The specific preparation method is as follows:

[0315] Using the same graphite and silicon-containing material particles as in Example 1, graphite, silicon-containing material particles, and phenolic resin were mixed in a ratio of 9:1:1.2 and placed in the feed hopper of a spraying device. Under nitrogen protection, the air pressure in feed hopper 2 was set to 150 kPa, the inlet air temperature was 210°C, and the outlet air temperature was 170°C to obtain secondary particles.

[0316] The secondary particles were placed in a heating chamber. Under a nitrogen atmosphere, the heating chamber was first heated to 660°C. Then, a mixed gas was introduced at a volume ratio of nitrogen to acetylene gas of 1:2. The mixture was kept at this temperature for 0.5 hours. Carbon coating treatment was then performed on the surface of the secondary particles to obtain a silicon-carbon composite material.

[0317] Comparative Example 2

[0318] The battery in Comparative Example 2 was prepared using a similar method to the battery in Example 1, except that the silicon-carbon composite material was a direct mixture of silicon-containing material particles and graphite. The specific preparation method was as follows:

[0319] Using the same graphite and silicon-containing material particles as in Example 1, the graphite and silicon-containing material particles were dry-mixed evenly at a ratio of 9:1 to obtain a mixed powder.

[0320] II. Testing Methods

[0321] 1. Specific capacity testing of silicon-carbon composite materials

[0322] Cell fabrication: A button cell is fabricated, with lithium foil used as the positive electrode. The prepared silicon-carbon composite material, conductive carbon black, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC-Na) thickener are thoroughly mixed in a deionized water solvent system at a weight ratio of 95:2:2:1 to obtain a negative electrode slurry. This slurry is then uniformly coated onto a 13μm thick copper foil current collector at a coating speed of 25m / min and a coating oven temperature of 110℃. The negative electrode is then cold-pressed and slit to obtain the negative electrode sheet. In an argon-atmosphere glove box (H2O content <0.1ppm, O2 content <0.1ppm), lithium hexafluorophosphate (LiPF6) is dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC:DEC volume ratio 3:7) and stirred until homogeneous, yielding an electrolyte with a lithium salt concentration of 1mol / L. A 9μm polyethylene (PE) film is used as the separator. The above-mentioned positive electrode, separator, negative electrode, and electrolyte were assembled into a battery for testing.

[0323] Test Procedure: Under room temperature conditions, allow the battery to stand for 3 hours, then discharge it at a constant current of 0.05C until the voltage reaches 0.005V. Further discharge it at a constant current of 50μA until the voltage reaches 0.005V. Record the capacity at this point as the lithium intercalation capacity. Allow it to stand for 5 minutes, then charge it at a rate of 0.1C until the voltage reaches 0.8V. Record the capacity at this point as the delithiation capacity, which is the material capacity. The ratio of the delithiation capacity to the mass of the silicon-carbon composite material is the specific capacity of the silicon-carbon composite material.

[0324] 2. Battery room temperature cycle performance test

[0325] Test Procedure: At 25℃, allow the battery to stand for 30 minutes. Then, charge it at a 0.5C rate until the voltage reaches 4.2V. Further charge it at a constant voltage of 4.2V until the current reaches 0.05C. Allow it to stand for 5 minutes, then discharge it at a 0.5C rate until the voltage reaches 2.8V. The resulting capacity is recorded as the initial capacity C0. This constitutes one charge-discharge cycle. Repeat the above steps for the same battery, recording the discharge capacity Cn at each cycle. The battery capacity retention rate after each cycle is Pn = Cn / C0 * 100%, continuing until Pn ≦ 80%. Stop the test and record the number of cycles at this point.

[0326] 3. Battery high-temperature storage performance test

[0327] Test conditions: At 60℃, the fully charged battery cells are stored and the capacity is tested every 30 days until the capacity decays to 80% of the initial capacity. The number of storage days at this point is recorded.

[0328] Test Procedure: Let the battery rest for 30 minutes, then discharge it at a 0.5C rate to 2.8V, let it rest for 5 minutes, then charge it at a 0.5C rate to 4.2V, and further charge it at a constant voltage of 4.2V until the current reaches 0.05C, let it rest for 5 minutes, and then discharge it at a 0.5C rate to 2.8V. This is the capacity test procedure, and the discharge capacity is recorded each time. Let the battery rest for another 5 minutes, then charge it at a 0.5C rate to 4.2V, and further charge it at a constant voltage of 4.2V until the current reaches 0.05C. This fully charges the cell. Then place it in a 60℃ temperature chamber, and test the capacity after 30 days according to the above procedure.

[0329] The capacity retention rate (%) after n days of storage is calculated as (discharge capacity on day n / initial discharge capacity on day 0) × 100%. The test is stopped when the capacity retention rate is ≤ 80%, and the number of storage days at this point is recorded. A fitted curve is plotted with the number of days on the x-axis and the capacity retention rate on the y-axis to obtain the number of storage days when the capacity retention rate is 80%.

[0330] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0331] Batteries for each embodiment and comparative example were prepared according to the above method, and various performance parameters were measured. The results are shown in the table below.

[0332] As shown in Table 2, the internal region of the silicon-carbon composite material is mainly composed of silicon particles, while the external region is mainly composed of graphite particles. This structure can improve the high-temperature storage performance and cycle stability of the battery, while the silicon-carbon composite material also has excellent capacity.

[0333] Table 2

[0334]

[0335]

[0336] As shown in Tables 3 and 4, when the mass percentage of silicon in the region r / 2 from the geometric center of the silicon-carbon composite material is greater than or equal to 30%, the silicon-carbon composite material exhibits excellent specific capacity, and the battery demonstrates excellent high-temperature storage performance and cycle stability. When the Dv50 of the silicon-carbon composite material is less than or equal to 16 μm, the battery exhibits good high-temperature storage performance and cycle stability.

[0337] Table 3

[0338]

[0339] Table 4

[0340]

[0341] As shown in Table 5, when the carbon content in the region extending inward from the surface of the silicon-carbon composite material is greater than or equal to 80%, the battery exhibits excellent high-temperature storage performance and cycle stability, while the silicon-carbon composite material also possesses excellent specific capacity.

[0342] Table 5

[0343]

[0344]

[0345] As shown in Table 6, when the porosity of silicon-carbon composite materials is 20%-45%, silicon-carbon composite materials have excellent specific capacity, and the batteries have excellent high-temperature storage performance and cycle stability.

[0346] Table 6

[0347]

[0348] As can be seen from the comparison between Examples 1 and 11 in Table 7, when the Dv50 of the silicon-containing material particles is greater than that of the graphite particles, the high-temperature storage performance of the battery can be improved. As can be seen from the comparison between Examples 1 and 12 in Table 7, the pore volume of the carbon substrate micropores in the silicon-containing material particles is greater than or equal to 0.5 cm³. 3 At / g, silicon-carbon composite materials have superior specific capacity, and the battery combines excellent high-temperature storage performance and cycle performance.

[0349] Table 7

[0350]

[0351] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A silicon-carbon composite material, characterized in that, The silicon-carbon composite material includes an internal region and an external region. The internal region is mainly composed of silicon-containing material particles, and the external region is mainly composed of carbon-based material particles. The silicon element mass ratio in the region r / 2 away from the geometric center of the silicon-carbon composite material is greater than or equal to 30%, and the carbon element mass ratio in the region where the outer surface of the silicon-carbon composite material extends inward at a distance of r / 2 is greater than or equal to 80%, where r represents the minor diameter of the silicon-carbon composite material.

2. The silicon-carbon composite material according to claim 1, characterized in that, The number of silicon-containing material particles in the internal region is less than or equal to 3.

3. The silicon-carbon composite material according to claim 1, characterized in that, The number of silicon-containing material particles in the internal region is 1-2.

4. The silicon-carbon composite material according to claim 1, characterized in that, The silicon content of the silicon-carbon composite material is 35%-45% in the region r / 2 from the geometric center, where r represents the minor axis of the silicon-carbon composite material.

5. The silicon-carbon composite material according to claim 1, characterized in that, The carbon content in the region extending from the outer surface of the silicon-carbon composite material to the inner surface by a distance of r / 2 is 90%-100%, where r represents the minor diameter of the silicon-carbon composite material.

6. The silicon-carbon composite material according to any one of claims 1 to 5, characterized in that, The outer region of the silicon-carbon composite material also includes an amorphous carbon coating layer.

7. The silicon-carbon composite material according to any one of claims 1 to 5, characterized in that, The Dv50 of the silicon-containing material particles is greater than or equal to the Dv50 of the carbon-based material particles.

8. The silicon-carbon composite material according to any one of claims 1 to 5, characterized in that, The Dv50 of the silicon-containing material particles is less than or equal to 5 μm; and / or, The Dv50 of the carbon-based material particles is less than or equal to 5 μm.

9. The silicon-carbon composite material according to any one of claims 1 to 5, characterized in that, The silicon-containing material particles include at least one of elemental silicon, silicon-oxygen materials, silicon-carbon materials, and silicon-metal alloys; And / or, the carbon-based material particles include at least one of artificial graphite and natural graphite.

10. The silicon-carbon composite material according to any one of claims 1 to 5, characterized in that, The silicon-containing material particles include silicon-carbon materials; The carbon-based material particles include artificial graphite.

11. The silicon-carbon composite material according to claim 1, characterized in that, The silicon-containing material particles include a carbon substrate with a porous structure and a silicon-based material disposed in the porous structure of the carbon substrate.

12. The silicon-carbon composite material according to claim 11, characterized in that, The carbon substrate includes micropores with a pore size of less than 2 nm, mesopores with a pore size of 2 nm to 50 nm, and macropores with a pore size of more than 50 nm.

13. The silicon-carbon composite material according to claim 12, characterized in that, The pore volume of the micropores is greater than or equal to 0.5 cm³. 3 / g.

14. The silicon-carbon composite material according to claim 13, characterized in that, The pore volume of the micropore is 0.6 cm³. 3 / g-0.9cm 3 / g.

15. The silicon-carbon composite material according to any one of claims 11 to 14, characterized in that, The average pore size of the carbon substrate is less than or equal to 5 nm.

16. The silicon-carbon composite material according to claim 15, characterized in that, The carbon substrate has an average pore size of 1 nm to 3.5 nm.

17. The silicon-carbon composite material according to any one of claims 11 to 14, characterized in that, The specific surface area of ​​the carbon substrate is greater than or equal to 1200 m². 2 / g.

18. The silicon-carbon composite material according to claim 17, characterized in that, The specific surface area of ​​the carbon substrate is 1500 m². 2 / g-1800m 2 / g.

19. The silicon-carbon composite material according to any one of claims 11 to 14, characterized in that, The silicon-based material includes at least one of elemental silicon, silicon-oxygen materials, silicon-carbon materials, and silicon-metal alloys; the carbon substrate includes at least one of graphite, soft carbon, and hard carbon.

20. The silicon-carbon composite material according to any one of claims 11 to 14, characterized in that, The silicon-based material includes silicon grains.

21. The silicon-carbon composite material according to claim 20, characterized in that, The size of the silicon grains is less than or equal to 10 nm.

22. The silicon-carbon composite material according to claim 20, characterized in that, The size of the silicon grains is less than or equal to 3 nm.

23. The silicon-carbon composite material according to any one of claims 1 to 5, characterized in that, The porosity of the silicon-carbon composite material is 20%-45%.

24. The silicon-carbon composite material according to claim 23, characterized in that, The porosity of the silicon-carbon composite material is 20%-35%.

25. The silicon-carbon composite material according to any one of claims 1 to 5, characterized in that, The silicon-carbon composite material also satisfies at least one of the following conditions: (1) The volume distribution particle size Dv50 of the silicon-carbon composite material is less than or equal to 16 μm; (2) The particle size distribution (Dv90-Dv10) / Dv50 of the silicon-carbon composite material is 0.5-1.8; (3) The powder compaction density of the silicon-carbon composite material at 49000N is 0.7 g / cm³. 3 -1.3g / cm 3 ; (4) The specific surface area of ​​the silicon-carbon composite material is less than or equal to 6 m². 2 / g.

26. The silicon-carbon composite material according to claim 25, characterized in that, The silicon-carbon composite material also satisfies at least one of the following conditions: (1) The volume distribution particle size Dv50 of the silicon-carbon composite material is 8μm-16μm; (2) The particle size distribution (Dv90-Dv10) / Dv50 of the silicon-carbon composite material is 0.8-1.5; (3) The powder compaction density of the silicon-carbon composite material at 49000N is 0.95 g / cm³. 3 -1.1g / cm 3 ; (4) The specific surface area of ​​the silicon-carbon composite material is less than or equal to 4.5 m². 2 / g.

27. A method for preparing a silicon-carbon composite material, characterized in that, Includes the following steps: We provide silicon-containing material particles and carbon-based material particles; The silicon-containing material particles and the binder are subjected to a first spray granulation process to obtain a first intermediate product; The silicon-carbon composite material is prepared by spraying carbon-based material particles onto the surface of the first intermediate product and performing a second spray granulation. The silicon-carbon composite material includes an internal region and an external region. The internal region is mainly composed of silicon-containing material particles, and the external region is mainly composed of carbon-based material particles. The silicon element mass ratio in the region r / 2 away from the geometric center of the silicon-carbon composite material is greater than or equal to 30%, and the carbon element mass ratio in the region where the outer surface of the silicon-carbon composite material extends inward at a distance of r / 2 is greater than or equal to 80%, where r represents the minor diameter of the silicon-carbon composite material.

28. The preparation method according to claim 27, characterized in that, The silicon-containing material particles are prepared through the following steps: A gas containing a silicon precursor is supplied to a carbon substrate with a porous structure; Silicon-based materials are generated from the silicon precursor and attached to the porous structure by chemical vapor deposition, thus obtaining silicon-containing material particles.

29. The preparation method according to claim 27 or 28, characterized in that, The mass ratio of the silicon-containing material particles to the binder is 1:2-2:1; and / or, The mass ratio of the silicon-containing material particles to the carbon-based material particles is 1:12-1:

6.

30. The preparation method according to claim 27 or 28, characterized in that, The first spray granulation satisfies at least one of the following conditions: (1) The temperature difference between the inlet air temperature and the outlet air temperature shall not exceed 60℃; (2) The inlet air temperature is 110℃-150℃; (3) The outlet air temperature is 50℃-90℃; (4) The feed air pressure is 250KPa-350KPa.

31. The preparation method according to claim 30, characterized in that, The first spray granulation meets the following requirements: the feed air pressure is 280KPa-320KPa.

32. The preparation method according to claim 27 or 28, characterized in that, The second spray granulation satisfies at least one of the following conditions: (1) The temperature difference between the inlet air temperature and the outlet air temperature is 20℃-40℃; (2) The air inlet temperature is 170℃-280℃; (3) The outlet air temperature is 130℃-240℃; (4) The feed air pressure is 150KPa-260KPa.

33. The preparation method according to claim 32, characterized in that, The second spray granulation meets the following requirements: the feed air pressure is 180KPa-210KPa.

34. The preparation method according to claim 27 or 28, characterized in that, The preparation method of the silicon-carbon composite material further includes: After the second spray granulation, a gaseous carbon source is introduced, and carbonization is carried out after gas phase coating to obtain the silicon-carbon composite material.

35. The preparation method according to claim 34, characterized in that, The introduced gaseous carbon source, after gas-phase coating and carbonization, yields the silicon-carbon composite material that satisfies at least one of the following conditions: (1) The gaseous carbon source includes gaseous hydrocarbons; (2) The carbonization temperature is 400℃-800℃; (3) The carbonization time is 0.2h-2h; (4) The protective gas during the carbonization process is nitrogen or argon.

36. The preparation method according to claim 34, characterized in that, The introduced gaseous carbon source, after gas-phase coating and carbonization, yields the silicon-carbon composite material that satisfies the following: (1) The gaseous carbon source includes at least one of methane, ethylene, and acetylene; (2) The protective gas during the carbonization process is nitrogen or argon, and the gas flow ratio of the carbon source to the protective gas is 1:5 to 1:1.

5.

37. The preparation method according to any one of claims 27 or 28, characterized in that, The adhesive includes at least one of phenolic resin, styrene-butadiene rubber, polyacrylic acid, carboxymethyl cellulose, sodium alginate, carboxymethyl chitosan, polyacrylonitrile, and polyacryl alcohol.

38. A secondary battery, characterized in that, The secondary battery includes a negative electrode sheet, which comprises a silicon-carbon composite material according to any one of claims 1 to 26 or a silicon-carbon composite material prepared by any one of claims 27 to 37.

39. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 38.

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